Snail Gets Spots to Fool Predators

Below:

Next story in Science

A freshwater snail common in ponds across Europe can adjust its
pigmentation in response to certain environmental stressors, new
research suggests.

Radix balthica, spanning less than a half-inch (0.8
centimeters) in length, sports dark body pigmentation that is
visible through its translucent yellow shell. Individuals vary in
skin pattern, with some speckled with dark spots and others
covered in a more uniformly dark pattern.

Researchers have thought the snail's variable coloring was
genetically predetermined, and didn't change during the snail's
life. But new research from a team at Lund University in Sweden
has shown that the presence of predators and the intensity of
damaging UV radiation from the sun do, indeed, influence their
color coats. [ Amazing
Mollusks: Images of Strange & Slimy Snails ]

"[Previous studies] tried to use these patterns to distinguish
between populations, but what we found was the snails from the
same pond can look very different," said study researcher Johan
Ahlgren. "One single snail can express all of these different
morphs."

Physically morphing in response to environmental cues — a trait
called
phenotypic plasticity because the physical expression of
an organism's genes is called its phenotype — occurs within many
plants and animals, and has even been shown within R.
balthica for other traits, such as shell shape. However,
pigmentation plasticity, or changeability, had not yet been shown
in this species, the researchers say.

To determine how different environmental cues affect the snail's
skin pattern, the team tested a random sampling of newly hatched
snails under four conditions, including exposure to chemical
cues of a predatory fish, exposure to UV light, exposure to
both a predatory cue and UV light, and a control with neither
environmental stressor.

The team measured the snails' pigmentation after eight weeks
under these conditions. They found predatory cues induced spotted
patterns, which would provide camouflage against a pebbly pond
floor, whereas any exposure to UV radiation — with or without the
predatory cue — induced a darker, less complex pigmentation that
likely protects
the snail from the damaging effects of radiation. The finding
suggests protection against radiation takes precedence over
protection against predators.

Whether the snails morph multiple times during a lifetime remains
unclear, but the team hopes to address this question in future
research, Ahlgren said.

The findings are not entirely unexpected, said Anurag Agrawal, an
ecology and evolutionary biology researcher at Cornell University
who was not involved in the study, since many animals show
similar phenotypic plasticity. Still, this case adds one more
valuable example for biologists to consider how such plasticity
can vary across the animal kingdom.

"One thing that is interesting about the study is that there are
two very divergent environmental cues that influence the same
phenotype," Agrawal said. "I think that's a nice
contribution. When we have different environmental cues that pull
[an organism] in two directions, how does the organism decide
which [phenotype] it is going to utilize? Those are important
questions."

The findings are detailed today (Sept. 17) in the journal Biology
Letters.